### Browsing by Author "Peltonen, Joonas T."

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Item Bolometric detection of Josephson inductance in a highly resistive environment(Nature Publishing Group, 2023-12) Subero, Diego; Maillet, Olivier; Golubev, Dmitry S.; Thomas, George; Peltonen, Joonas T.; Karimi, Bayan; Marín-Suárez, Marco; Yeyati, Alfredo Levy; Sánchez, Rafael; Park, Sunghun; Pekola, Jukka P.; Department of Applied Physics; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Universidad Autónoma de Madrid; Université Paris-SaclayThe Josephson junction is a building block of quantum circuits. Its behavior, well understood when treated as an isolated entity, is strongly affected by coupling to an electromagnetic environment. In 1983, Schmid predicted that a Josephson junction shunted by a resistance exceeding the resistance quantum R Q = h/4e 2 ≈ 6.45 kΩ for Cooper pairs would become insulating since the phase fluctuations would destroy the coherent Josephson coupling. However, recent microwave measurements have questioned this interpretation. Here, we insert a small Josephson junction in a Johnson-Nyquist-type setup where it is driven by weak current noise arising from thermal fluctuations. Our heat probe minimally perturbs the junction’s equilibrium, shedding light on features not visible in charge transport. We find that the Josephson critical current completely vanishes in DC charge transport measurement, and the junction demonstrates Coulomb blockade in agreement with the theory. Surprisingly, thermal transport measurements show that the Josephson junction acts as an inductor at high frequencies, unambiguously demonstrating that a supercurrent survives despite the Coulomb blockade observed in DC measurements.Item Determining the parameters of a random telegraph signal by digital low pass filtering(2018-06-11) Singh, Shilpi; Mannila, Elsa T.; Golubev, Dmitry S.; Peltonen, Joonas T.; Pekola, Jukka P.; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Department of Applied PhysicsWe propose a method to determine the switching rates of a random telegraph signal. We apply digital low pass filtering with varying bandwidths to the raw signal, evaluate the cumulants of the resulting distributions, and compare them with the analytical prediction. This technique is useful in the case of a slow detector with response time comparable to the time interval between the switching events. We demonstrate the efficiency of this method by analyzing random telegraph signals generated by individual charge tunneling events in metallic single-electron transistors.Item Electric field control of radiative heat transfer in a superconducting circuit(Nature Publishing Group, 2020-08-28) Maillet, Olivier; Subero, Diego; Peltonen, Joonas T.; Golubev, Dmitry S.; Pekola, Jukka P.; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and DevicesHeat is detrimental for the operation of quantum systems, yet it fundamentally behaves according to quantum mechanics, being phase coherent and universally quantum-limited regardless of its carriers. Due to their robustness, superconducting circuits integrating dissipative elements are ideal candidates to emulate many-body phenomena in quantum heat transport, hitherto scarcely explored experimentally. However, their ability to tackle the underlying full physical richness is severely hindered by the exclusive use of a magnetic flux as a control parameter and requires complementary approaches. Here, we introduce a dual, magnetic field-free circuit where charge quantization in a superconducting island enables thorough electric field control. We thus tune the thermal conductance, close to its quantum limit, of a single photonic channel between two mesoscopic reservoirs. We observe heat flow oscillations originating from the competition between Cooper-pair tunnelling and Coulomb repulsion in the island, well captured by a simple model. Our results highlight the consequences of charge-phase conjugation on heat transport, with promising applications in thermal management of quantum devices and design of microbolometers.Item An electron turnstile for frequency-to-power conversion(Nature Publishing Group, 2022-03) Marín-Suárez, Marco; Peltonen, Joonas T.; Golubev, Dmitry S.; Pekola, Jukka P.; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsSingle-electron transport relates an operation frequency f to the emitted current I through the electron charge e as I = ef (refs. 1–5). Similarly, direct frequency-to-power conversion (FPC) links both quantities through a known energy. FPC is a natural candidate for a power standard resorting to the most basic definition of the watt: energy emitted per unit of time. The energy is traceable to Planck’s constant and the time is in turn traceable to the unperturbed ground state hyperfine transition frequency of the caesium 133 atom. Hence, FPC comprises a simple and elegant way to realize the watt6. In this spirit, single-photon emission7,8 and detection9 at known rates have been proposed as radiometric standards and experimentally realized10–14. However, power standards are so far only traceable to electrical units, that is, to the volt and the ohm6,15–17. In this Letter, we demonstrate an alternative proposal based on solid-state direct FPC using a hybrid single-electron transistor (SET). The SET injects n (integer) quasi-particles (QPs) per cycle into the two superconducting leads with discrete energies close to their superconducting gap Δ, even at zero source-drain voltage. Furthermore, the application of a bias voltage can vary the distribution of the power among the two leads, allowing for an almost equal power injection nΔf into the two. While in single-electron transport current is related to a fixed universal constant (e), in our approach Δ is a material-dependent quantity. We estimate that under optimized conditions errors can be well below 1%.Item Electron-phonon coupling of epigraphene at millikelvin temperatures measured by quantum transport thermometry(AMER INST PHYSICS, 2021-03-08) Karimi, Bayan; He, Hans; Chang, Yu Cheng; Wang, Libin; Pekola, Jukka P.; Yakimova, Rositsa; Shetty, Naveen; Peltonen, Joonas T.; Lara-Avila, Samuel; Kubatkin, Sergey; Centre of Excellence in Quantum Technology, QTF; Chalmers University of Technology; Department of Applied Physics; Linköping University; Quantum Phenomena and DevicesWe investigate the basic charge and heat transport properties of charge neutral epigraphene at sub-kelvin temperatures, demonstrating a nearly logarithmic dependence of electrical conductivity over more than two decades in temperature. Using graphene's sheet conductance as an in situ thermometer, we present a measurement of electron-phonon heat transport at mK temperatures and show that it obeys the T4 dependence characteristic for a clean two-dimensional conductor. Based on our measurement, we predict the noise-equivalent power of ∼ 10 - 22 W / Hz of the epigraphene bolometer at the low end of achievable temperatures.Item Extreme reductions of entropy in an electronic double dot(American Physical Society, 2019-03-18) Singh, Shilpi; Roldan, Edgar; Neri, Izaak; Khaymovich, Ivan M.; Golubev, Dmitry S.; Maisi, Ville F.; Peltonen, Joonas T.; Juelicher, Frank; Pekola, Jukka P.; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Center for Advancing Electronics Dresden; Max Planck Institute for the Physics of Complex Systems; Lund UniversityWe experimentally study negative fluctuations of stochastic entropy production in an electronic double dot operating in nonequilibrium steady-state conditions. We record millions of random electron tunneling events at different bias points, thus collecting extensive statistics. We show that for all bias voltages, the experimental average values of the minima of stochastic entropy production lie above -k(B), where k(B) is the Boltzmann constant, in agreement with recent theoretical predictions for nonequilibrium steady states. Furthermore, we also demonstrate that the experimental cumulative distribution of the entropy production minima is bounded, at all times and for all bias voltages, by a universal expression predicted by the theory. We also extend our theory by deriving a general bound for the average value of the maximum heat absorbed by a mesoscopic system from the environment and compare this result with experimental data. Finally, we show by numerical simulations that these results are not necessarily valid under nonstationary conditions.Item Fast and accurate Cooper pair pump(American Physical Society, 2019-12-16) Erdman, Paolo A.; Taddei, Fabio; Peltonen, Joonas T.; Fazio, Rosario; Pekola, Jukka P.; Scuola Normale Superiore di Pisa; Consiglio Nazionale delle Ricerche (CNR); Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsWe propose a method to perform accurate and fast charge pumping in superconducting nanocircuits. Combining topological properties and quantum control techniques based on shortcuts to adiabaticity, we show that it is theoretically possible to achieve perfectly quantized charge pumping at any finite-speed driving. Model-specific errors may still arise due the difficulty of implementing the exact control. We thus assess this and other practical issues in a specific system comprised of three Josephson junctions. Using realistic system parameters, we show that our scheme can improve the pumping accuracy of this device by various orders of magnitude. Possible metrological perspectives are discussed.Item Heat rectification via a superconducting artificial atom(Nature Publishing Group, 2020-12-01) Senior, Jorden; Gubaydullin, Azat; Karimi, Bayan; Peltonen, Joonas T.; Ankerhold, Joachim; Pekola, Jukka P.; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and DevicesIn developing technologies based on superconducting quantum circuits, the need to control and route heating is a significant challenge in the experimental realisation and operation of these devices. One of the more ubiquitous devices in the current quantum computing toolbox is the transmon-type superconducting quantum bit, embedded in a resonator-based architecture. In the study of heat transport in superconducting circuits, a versatile and sensitive thermometer is based on studying the tunnelling characteristics of superconducting probes weakly coupled to a normal-metal island. Here we show that by integrating superconducting quantum bit coupled to two superconducting resonators at different frequencies, each resonator terminated (and thermally populated) by such a mesoscopic thin film metal island, one can experimentally observe magnetic flux-tunable photonic heat rectification between 0 and 10%.Item Interplay of the Inverse Proximity Effect and Magnetic Field in Out-of-Equilibrium Single-Electron Devices(2017-05-26) Nakamura, Shuji; Pashkin, Yuri A.; Taupin, Mathieu; Maisi, Ville F.; Khaymovich, Ivan M.; Mel'Nikov, Alexander S.; Peltonen, Joonas T.; Pekola, Jukka P.; Okazaki, Yuma; Kashiwaya, Satoshi; Kawabata, Shiro; Vasenko, Andrey S.; Tsai, Jaw-Shen; Kaneko, Nobu Hisa; National Institute of Advanced Industrial Science and Technology; Lancaster University; Vienna University of Technology; Department of Applied Physics; Max Planck Institute for the Physics of Complex Systems; Russian Academy of Sciences; Higher School of Economics; RIKENWe show that a weak external magnetic field affects significantly nonequilibrium quasiparticle (QP) distributions under the conditions of the inverse proximity effect, using the single-electron hybrid turnstile as a generic example. Inverse proximity suppresses the superconducting gap in superconducting leads in the vicinity of turnstile junctions, thus, trapping hot QPs in this region. An external magnetic field creates additional QP traps in the leads in the form of vortices or regions with a reduced superconducting gap resulting in the release of QPs away from the junctions. We present clear experimental evidence of the interplay of the inverse proximity effect and magnetic field revealing itself in the superconducting gap enhancement and significant improvement of the turnstile characteristics. The observed interplay and its theoretical explanation in the context of QP overheating are important for various superconducting and hybrid nanoelectronic devices, which find applications in quantum computation, photon detection, and quantum metrology.Item Microwave quantum diode(Nature Publishing Group, 2024-01-20) Upadhyay, Rishabh; Golubev, Dmitry S.; Chang, Yu Cheng; Thomas, George; Guthrie, Andrew; Peltonen, Joonas T.; Pekola, Jukka P.; Department of Applied Physics; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTFThe fragile nature of quantum circuits is a major bottleneck to scalable quantum applications. Operating at cryogenic temperatures, quantum circuits are highly vulnerable to amplifier backaction and external noise. Non-reciprocal microwave devices such as circulators and isolators are used for this purpose. These devices have a considerable footprint in cryostats, limiting the scalability of quantum circuits. As a proof-of-concept, here we report a compact microwave diode architecture, which exploits the non-linearity of a superconducting flux qubit. At the qubit degeneracy point we experimentally demonstrate a significant difference between the power levels transmitted in opposite directions. The observations align with the proposed theoretical model. At − 99 dBm input power, and near the qubit-resonator avoided crossing region, we report the transmission rectification ratio exceeding 90% for a 50 MHz wide frequency range from 6.81 GHz to 6.86 GHz, and over 60% for the 250 MHz range from 6.67 GHz to 6.91 GHz. The presented architecture is compact, and easily scalable towards multiple readout channels, potentially opening up diverse opportunities in quantum information, microwave read-out and optomechanics.Item Optimal Probabilistic Work Extraction beyond the Free Energy Difference with a Single-Electron Device(American Physical Society, 2019-04-18) Maillet, Olivier; Erdman, Paolo A.; Cavina, Vasco; Bhandari, Bibek; Mannila, Elsa T.; Peltonen, Joonas T.; Mari, Andrea; Taddei, Fabio; Jarzynski, Christopher; Giovannetti, Vittorio; Pekola, Jukka P.; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; CNR-ENEA-EURATOM Association; University of Maryland, College Park; National Enterprise for nanoScience and nanoTechnologyWe experimentally realize protocols that allow us to extract work beyond the free energy difference from a single-electron transistor at the single thermodynamic trajectory level. With two carefully designed out-of-equilibrium driving cycles featuring kicks of the control parameter, we demonstrate work extraction up to large fractions of kBT or with probabilities substantially greater than 1/2, despite the zero free energy difference over the cycle. Our results are explained in the framework of nonequilibrium fluctuation relations. We thus show that irreversibility can be used as a resource for optimal work extraction even in the absence of feedback from an external operator.Item Optimized Proximity Thermometer for Ultrasensitive Detection(American Physical Society, 2020-05-01) Karimi, Bayan; Nikolic, Danilo; Tuukkanen, Tuomas; Peltonen, Joonas T.; Belzig, Wolfgang; Pekola, Jukka P.; Centre of Excellence in Quantum Technology, QTF; University of Konstanz; Department of Applied PhysicsWe present a set of experiments to optimize the performance of a noninvasive thermometer based on proximity superconductivity. Current through a standard tunnel junction between an aluminum superconductor and a copper electrode is controlled by the strength of the proximity induced to this normal metal, which in turn is determined by the position of a direct superconducting contact from the tunnel junction. Several devices with different distances are tested. We develop a theoretical model based on Usadel equations and dynamic Coulomb blockade that reproduces the measured results and yields a tool to calibrate the thermometer and to optimize it further in future experiments. We also propose an analytic formula that reproduces the experimental data for a wide range of temperatures.Item Photonic heat transport in three terminal superconducting circuit(Nature Publishing Group, 2022-03-23) Gubaydullin, Azat; Thomas, George; Golubev, Dmitry S.; Lvov, Dmitrii; Peltonen, Joonas T.; Pekola, Jukka P.; Department of Applied Physics; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTFWe report an experimental realization of a three-terminal photonic heat transport device based on a superconducting quantum circuit. The central element of the device is a flux qubit made of a superconducting loop containing three Josephson junctions, which can be tuned by magnetic flux. It is connected to three resonators terminated by resistors. By heating one of the resistors and monitoring the temperatures of the other two, we determine photonic heat currents in the system and demonstrate their tunability by magnetic field at the level of 1 aW. We determine system parameters by performing microwave transmission measurements on a separate nominally identical sample and, in this way, demonstrate clear correlation between the level splitting of the qubit and the heat currents flowing through it. Our experiment is an important step towards realization of heat transistors, heat amplifiers, masers pumped by heat and other quantum heat transport devices.Item Radio-Frequency Coulomb-Blockade Thermometry(American Physical Society, 2022-01-26) Blanchet, Florian; Chang, Yu Cheng; Karimi, Bayan; Peltonen, Joonas T.; Pekola, Jukka P.; Quantum Computing and Devices; Quantum Phenomena and Devices; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsWe present a scheme and demonstrate measurements of a Coulomb-blockade thermometer (CBT) in a microwave-transmission setup. The sensor is embedded in an LCR resonator, where R is determined by the conductance of the junction array of the CBT. A transmission measurement yields a signal that is directly proportional to the conductance of the CBT, thus enabling the calibration-free operation of the thermometer. This is verified by measuring an identical sensor simultaneously in the usual dc setup. The important advantage of the rf measurement is its speed: the whole bias dependence of the CBT conductance can now be measured in a time of about 100 ms, which is 1000 times faster than in a standard dc measurement. The achieved noise-equivalent temperature of this rf primary measurement is about 1mK/Hz at the bath temperature T=200mK.Item Robust Strong-Coupling Architecture in Circuit Quantum Electrodynamics(American Physical Society, 2021-10-25) Upadhyay, Rishabh; Thomas, George; Chang, Yu Cheng; Golubev, Dmitry S.; Guthrie, Andrew; Gubaydullin, Azat; Peltonen, Joonas T.; Pekola, Jukka P.; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Department of Applied PhysicsWe report on a robust method to achieve strong coupling between a superconducting flux qubit and a high-quality quarter-wavelength coplanar waveguide resonator. We demonstrate the progression from the strong to ultrastrong coupling regime by varying the length of a shared inductive coupling element, ultimately achieving a qubit-resonator coupling strength of 655 MHz, 10% of the resonator frequency. We derive an analytical expression for the coupling strength in terms of circuit parameters and also discuss the maximum achievable coupling within this framework. We experimentally characterize flux qubits coupled to superconducting resonators using one- and two-tone spectroscopy methods, demonstrating excellent agreement with the proposed theoretical model.Item Suppression of Back-Tunneling Events in Hybrid Single-Electron Turnstiles by Source-Drain Bias Modulation(American Physical Society, 2023-04) Marín-Suárez, Marco; Pashkin, Yuri A.; Peltonen, Joonas T.; Pekola, Jukka P.; Quantum Phenomena and Devices; Lancaster University; Centre of Excellence in Quantum Technology, QTF; Department of Applied PhysicsThe accuracy of single-electron currents produced in hybrid turnstiles at high operation frequencies is, among other errors, limited by electrons tunneling in the wrong direction. Increasing the barrier transparency between the island and the leads, together with the source-drain bias, helps to suppress these events in a larger frequency range, although they lead to some additional errors. We experimentally demonstrate a driving scheme that suppresses tunneling in the wrong direction, thus extending the range of frequencies for generating accurate single-electron currents. The main feature of this approach is an additional ac signal applied to the bias with frequency twice that applied to the gate electrode. This allows additional modulation of the island chemical potential. By using this approach under certain parameters, we improve the single-electron current accuracy by one order of magnitude. Finally, we show through experimentally contrasted calculations that our method can improve accuracy even in devices for which the usual gate driving gives errors of the order of 10-3 at high frequencies and can bring them under 5×10-4.Item Suppression of the critical current of a balanced superconducting quantum interference device(AIP Publishing, 2008) Kemppinen, Antti; Manninen, Antti J.; Möttönen, Mikko; Vartiainen, Juha J.; Peltonen, Joonas T.; Pekola, Jukka P.; Department of Applied Physics; Teknillisen fysiikan laitos; Perustieteiden korkeakoulu; School of ScienceWe present an experimental study of the magnetic flux dependence of the critical current of a balanced superconducting quantum interference device (SQUID) with three Josephson junctions in parallel. Unlike for ordinary direct current (dc) SQUIDs, the suppression of the critical current does not depend on the exact parameters of the Josephson junctions. The suppression is essentially limited only by the inductances of the SQUID loops. We demonstrate a critical current suppression ratio of higher than 300 in a balanced SQUID with a maximum critical current 30nA .Item Tunable photonic heat transport in a quantum heat valve(2018) Ronzani, Alberto; Karimi, Bayan; Senior, Jorden; Chang, Yu Cheng; Peltonen, Joonas T.; Chen, Chii Dong; Pekola, Jukka P.; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and DevicesQuantum thermodynamics is emerging both as a topic of fundamental research and as a means to understand and potentially improve the performance of quantum devices1–10. A prominent platform for achieving the necessary manipulation of quantum states is superconducting circuit quantum electrodynamics (QED)11. In this platform, thermalization of a quantum system12–15 can be achieved by interfacing the circuit QED subsystem with a thermal reservoir of appropriate Hilbert dimensionality. Here we study heat transport through an assembly consisting of a superconducting qubit16 capacitively coupled between two nominally identical coplanar waveguide resonators, each equipped with a heat reservoir in the form of a normal-metal mesoscopic resistor termination. We report the observation of tunable photonic heat transport through the resonator–qubit–resonator assembly, showing that the reservoir-to-reservoir heat flux depends on the interplay between the qubit–resonator and the resonator–reservoir couplings, yielding qualitatively dissimilar results in different coupling regimes. Our quantum heat valve is relevant for the realization of quantum heat engines17 and refrigerators, which can be obtained, for example, by exploiting the time-domain dynamics and coherence of driven superconducting qubits18,19. This effort would ultimately bridge the gap between the fields of quantum information and thermodynamics of mesoscopic systems.Item Universal First-Passage-Time Distribution of Non-Gaussian Currents(American Physical Society, 2019-06-13) Singh, Shilpi; Menczel, Paul; Golubev, Dmitry S.; Khaymovich, Ivan M.; Peltonen, Joonas T.; Flindt, Christian; Saito, Keiji; Roldán, Édgar; Pekola, Jukka P.; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; Quantum Transport; Keio University; Abdus Salam International Centre for Theoretical Physics; Max Planck InstituteWe investigate the fluctuations of the time elapsed until the electric charge transferred through a conductor reaches a given threshold value. For this purpose, we measure the distribution of the first-passage times for the net number of electrons transferred between two metallic islands in the Coulomb blockade regime. Our experimental results are in excellent agreement with numerical calculations based on a recent theory describing the exact first-passage-time distributions for any nonequilibrium stationary Markov process. We also derive a simple analytical approximation for the first-passage-time distribution, which takes into account the non-Gaussian statistics of the electron transport, and show that it describes the experimental distributions with high accuracy. This universal approximation describes a wide class of stochastic processes, and can be used beyond the context of mesoscopic charge transport. In addition, we verify experimentally a fluctuation relation between the first-passage-time distributions for positive and negative thresholds.Item Utilization of the superconducting transition for characterizing low-quality-factor superconducting resonators(AMER INST PHYSICS, 2019-07-08) Chang, Yu Cheng; Karimi, Bayan; Senior, Jorden; Ronzani, Alberto; Peltonen, Joonas T.; Goan, Hsi Sheng; Chen, Chii Dong; Pekola, Jukka P.; Department of Applied Physics; Centre of Excellence in Quantum Technology, QTF; Quantum Phenomena and Devices; National Taiwan UniversityCharacterizing superconducting microwave resonators with highly dissipative elements is a technical challenge, but a requirement for implementing and understanding the operation of hybrid quantum devices involving dissipative elements, e.g., for thermal engineering and detection. We present experiments on λ/4 superconducting niobium coplanar waveguide resonators, terminating at the antinode by a dissipative copper microstrip via aluminum leads, such that the resonator response is difficult to measure in a typical microwave environment. By measuring the transmission both above and below the superconducting transition of aluminum, we are able to isolate the resonance. We then experimentally verify this method with copper microstrips of increasing thicknesses, from 50 nm to 150 nm, and measure quality factors in the range of 10-67 in a consistent way.